rxjava 2 flapMap example in Android

Each successive flapMap takes the result from the previous one as the input, multiply it by an integer and passes it as a new input to the next flapMap. For example:
input: 2
1st flapMap: 2 * 2
2nd flapMap: 4 * 3
3rd flapMap: 12 * 4
Final result: 48